Photoabsorption of Nitrous Oxide through Rydberg States in the Bound and Continuum Spectral Regions: Main Ionization Channels

Photoionization cross sections and asymmetry parameters for the valence shell of methanol

Theoretical cross sections for photoionization of the methanol valence orbitals in covering a region up to 80 eV beyond the first ionization potential are reported. The molecular quantum defect orbital, MQDO, method, which has proved to be reliable in previous applications to molecular photoionization, has been used. To our knowledge, predictions of electronic partial cross section profiles on this molecule are made here for the first time, and we are not aware of any reported experimental data. Partial cross sections for production of parent and fragment ions of methanol have also been calculated and compared with previous measurements. In addition, the MQDO method has been used to calculate the angular distribution of photoelectrons for the valence orbitals of methanol over the 11-50 eV photon energy range. Our results are compared with experimental data, showing a good agreement in most cases. We hope that the present results might be of use in atmospheric and interstellar chemistry, where this molecule plays an important role.

Angular distribution of photoelectrons in small molecules: a molecular quantum defect calculation

The molecular quantum defect orbital (MQDO) method, previously used in the determination of molecular photoionization cross sections, is applied here to calculate the angular distribution of photoelectrons arising from the molecular photoionization. Calculations are performed for the ionization from outer valence orbitals of HF, H(2)O, NH(3), N(2)O, and H(2)CO molecules. The results are compared with previous measurements and with theoretical curves found in the literature. Profiles of the angular distribution parameter as a function of photoelectron energy covering a range from the photoionization threshold to 120 eV are presented for the above molecules. The energy dependence of the angular distributions predicted by the MQDO calculations agrees fairly well with predictions from more sophisticated theories and with observed results.

Theoretical study of spectral intensities of formaldehyde in the discrete and continuum regions

Theoretical absorption oscillator strengths for transitions involving Rydberg states in molecular formaldehyde as well as cross sections for photoionization Rydberg channels associated with the production of the lowest parent ion electronic state are reported. The calculations have been performed with the molecular quantum defect orbital (MQDO) method. A test on the MQDO f values has been its comparison with previous experiments and calculations and its compliance with the expected systematic trends along the Rydberg series. The use of the MQDO method as an alternative to ab initio methods, which find serious difficulties in calculating spectral intensities in formaldehyde, is proposed. We hope that the spectroscopic data, many of them reported here for the first time, may be useful for the interpretation of the vacuum ultraviolet spectrum of this molecule.

Photoinduced Electron-Transfer Reactions in Two Room-Temperature Ionic Liquids: 1-Butyl-3-methylimidazolium Hexafluorophosphate and 1-Octyl-3-methylimidazolium Hexafluorophosphate

Photoinduced electron transfer in two room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF(6)) and 1-octyl-3-methylimidazolium hexafluorophosphate (OMIM-PF(6)), has been investigated using steady-state fluorescence quenching of 9,10-dicyanoanthracene with a series of single electron donors. From these fluorescence quenching rates, reorganization energy (lambda) values and k(diff) values can be derived from a Rehm-Weller analysis. In many cases, these fluorescence quenching reactions occur at rates larger than what would be expected based on the Smoluchowski equation. In addition, lambda values of 10.1 kcal/mol and 16.3 kcal/mol for BMIM-PF(6) and OMIM-PF(6), respectively, have been determined.

The ν1 and ν2 vibrational bands of the OCCN radical detected through time-resolved Fourier transform IR emission spectroscopy

Through monitoring the IR emission from vibrationally excited radicals generated by exothermic photolysis reactions, the CN stretch (ν1) and the CO stretch (ν2) vibrational bands of the cyanooxomethyl radical (OCCN) have been observed for the first time at 2093 cm–1 and 1774 cm–1, respectively. The OCCN radical was produced through 193 nm photolysis of methyl cyanoformate (NCC(O)OCH3), carbonyl cyanide (NCC(O)CN), and pivaloyl cyanide (NCC(O)C(CH3)3). The IR emission spectra were recorded by using nanosecond time-resolved Fourier transform IR emission spectroscopy. Assignments of the spectral peaks were made based on observed time and pressure dependences of IR emission intensities, ab initio calculations, and two-dimensional cross-spectra correlation analysis. Key words: radical, cyanooxomethyl, OCCN, time-resolved vibrational spectroscopy, FTIR, substituted carbonyl dissociation reactions, two-dimensional cross-spectra correlation analysis